The invention relates to an apparatus for producing fine or small facing sand particles, in particular those of greensand, for the production of casting molds in metal foundry techniques, comprising a feed device, with which molding sand containing lumps can be passed to a refining means in a refining device.
In foundries, the so-called greensand molding sands are customarily reprocessed in mixers. These mixers normally operate according to the pan system with rollers or with turbine-type centrifugal separators and even with both systems.
Often, the molding sand prepared in this way is still not adequate to the requirements of the molding shop and so the molding sand is subsequently centrifuged.
Despite this procedure molding sand treated in this manner still contains lumps.
A molding sand containing lumps is not suitable for the production of finely contoured, filigrane casting molds since the casting molds which can be produced with this sand do not have any sharp outlines. It is therefore still necessary to pulverize the molding sand containing the lumps in addition.
One possibility of pulverizing this molding sand is described in DE-PS 12 88 754. The apparatus described in this publication is not capable of pulverizing the lumps of the molding sand to any satisfactory extent. In particular, the use of baffle boards for breaking up lumps has not brought the desired effect to any adequate degree since the lumps become compressed when beaten.
So far, the only satisfactory possibility of pulverizing the molding sand containing lumps is to first screen out the lumps in fine vibration sifters prior to coating the model and then break these lumps up. Such a screening of the sand containing lumps is extremely complex and mostly requires an additional operator who presses the lumps by hand onto the fine-meshed screens. Moreover, residue must be removed from the screens and, finally, such fine-meshed screens always tend to become clogged since the molding sand always shows a tendency to remain adhered to the meshing of the screen.
Facing sand particles are particles which comprise a quartz sand grain sheathed in clay or an agglomeration of several quartz sand grains each sheathed in clay and have, for example, in the fine state an average diameter of less than 1 mm or, even better, less than 0.5 mm, when the grain size of the quartz sand grains is from 0.04 to 0.4 mm.
The object underlying the invention is therefore to create an apparatus which enables finely pulverized facing sand particles to be produced from molding sand produced in a normal way but containing lumps.